The present invention relates to a hydraulically operated winch and a modulating control valve for operating the winch.
The winch is preferably of a type adapted for mounting upon a vehicle used in towing or logging applications. The winch is further contemplated as having a normally disengaged clutch which is hydraulically operable for driving a winch drum in rotation, a normally engaged brake being operable in opposition with the normally disengaged clutch to hold the winch drum against rotation for supporting a load or along to selectively permit rotation of the winch drum, for example in lowering a load, an additional clutch being normally engaged to provide a coupling between the winch drum and a drive shaft while being hydraulically disengageable to permit free wheeling of the winch drum.
A winch of this type is disclosed in greater detail by a co-pending U.S. patent application Ser. No. 334,354, now abandond, filed on Feb. 21, 1973 by Lyle F. Yates et al.
As noted in the co-pendng Patent application, it is desirable to provide for operation of such a winch system in a plurality of modes by a single control element. For example, it is desirable to synchronously operate the brake and the normally disengaged clutch in order to reel in a load, to hold the load by means of the brake and to selectively release the load by partially or completely disengaging the brake. In a further mode of operation, it is desirable to selectively disengage the normally engaged clutch to permit free wheeling of the winch drum. This mode of operation facilitates manual unwinding of cable from the winch drum for example by eliminating drag caused by internal components of the winch assembly.